Electronic relay



Feb., 14, 1950 J. G. lar-:ARQ ETAL,

ELECTRONIC RELAY -2 Sheets-Sheet 'l Filed Dec. 30, 1944 TQQ www" @ww SNN.

.H N S Feb. 14, 1950 J. G. lsf-:ARD ETAL ELECTRONIC RELAY 2 sheets-sheet 2 Filed Dec. 50, 1944 iatented 1:4,

ELECTRONIC RELAY Joseph G. Beard, Haddoneld, and Robert W. Harrelson, Masonville, N. J., and Alexander Kreithen, Philadelphia, Pa., assignors to Radio Corporation of America, a corporation of Dela- Ware Application December 30, 1944, Serial No. 570,706

6 Claims.

This invention relates to an electronic relay and motor control system. Among its objects is the provision of an improved relay which is free from the defects of prior art relays employing mechanical contacts and which is, in particular, more sensitive and less critical of adjustment than relays of the prior art, and which maintains its adjustment over a substantial period. Further objects include the provision of sensitive and efficient means for actuating an alternating current motor in response to minute variations in a controlling signal, and means for adjusting the limit of such variation which may be tolerated and for realizing full torque in the motor immediately such limit is exceeded. Other objects include the provision of a sensitive detector of minute variations in a controlling signal which absorbs a negligible amount of power from the circuit in which it is included, and of a gas tube circuit for producing a full-wave, alternating current in response to a variation in the con-v trolling signal. A specific object is the provision of improved means for maintaining a constant load on a radio communication transmitter notwithstanding variation in the frequency of the transmitted carrier signal.

According to the invention, a. circuit is provided for obtaining a pair of alternating voltages which are equal to each other in magnitude and phase, but which vary in opposite senses upon any variation in the controlling signal. Means are provided for adjusting the degree of variation .of the alternating voltages. These voltages are, in turn, applied to a gas tube network which is .energized by alternating voltage of the same fre- .quency and phase as the applied voltage and which produces a full-wave, alternating current of sufficient power to drive a motor, or for such other purpose as may be desired.

Reference may -be made to our U. S. Patent 2,455,646, application for which was iiled at the same time as this application was led.

In the accompanying drawing, Figure 1 is a diagram illustrating an application of one embodiment of the invention,

Figure 2 is a circuit diagram of the embodiment, the application of which is illustrated in Figure 1, and

Figure 3 is a diagram of another embodiment of the invention.

Figure 1 illustrates an application of Athe invention designed for use in a multi-stage, radio communication transmitter. This transmitter is intended to operate over a Wide ran-ge of car- Iier frequencies, say from two megacycles per second to twenty megacycles per second, and is completely automatically tuned; that is to say, operation of a single control varies the carrier frequency and also effects automatically a plurality of ancillary adjustments for operating the transmitter with eicency at a number of different frequencies within the range. The wide variation in frequency is accompanied by a correspondingly wide variation in the resistance and reactance of the antenna, and the controls must be capable of compensating for these variations.

In Figure 1 the final stage of the transmitter is represented by a power amplifier l0 having a tank circuit l2 which includes an inductor I4 coupled to an inductor I6 in an antenna circuit i8. A motor 20, controlled by a relay and motor control 22, is mechanically connected to vary the coupling between the tank and antenna circuits. The power amplier has a cathode circuit 24 which includes a resistor 26. When the transmitter is tuned to resonance at a particular frequency, current flowing in the anode circuit of the amplifier and, therefore, through the resistor 26 is at a minimum. When the frequency is changed this current increases and the voltage across resistor 26 increases correspondingly. The

purpose of the relay and motor control 22 is to operate the motor 20 in consequence of a change in voltage across resistor 26, and thereby to vary the coupling between the tank and antenna circuits.

Conventional polarized balanced relays with mechanical contacts and magnetic actuation of a moving armature are not suitable for the purpose indicated, because those which operate at a diierential of less than ten per cent from a mid value are expensive and extremely critical in adjustment and do not maintain their adjustment over any reasonable length of time. Prior art motor controls did not realize full torque in the motor immediately upon actuation and were notiv sufficiently positive and speedy for the applica-A tion described.

Figure 2 is a circuit diagram of the relay and motor control 22 of Figure 1 which may be employed in the place of prior art devices. There lay consists basically of a tube 28, and the motor control of four gas tubes 30, 32, 34 and 36, re-

spectively, each with its associated circuits. The

relay tube comprises two identical sections numbered i and 2, respectively, section l having a cathode 42, an anode 44 and a control electrode or grid 46; section 2 has similar electrodes 48',

50 and 52, respectively. The two cathodes 42 and 48 are connected to each other and to ground through a conductor 54, a resistor 56, a variable resistor 53 and a terminal 60, all as shown in Figure 2. The common cathode circuit is also connected to a terminal i8 between which and ground there is indicated a source of alternating current, which may conveniently be the commercial supply, having a frequency offsixty cycles per second.

The two sections of the relay tube 28 are shown as being contained in a single envelope and, in this form, may be of RCA Type 6SN7. Although such an arrangement is convenient, itis not essential for the purposes of the; invention, it being desirable that the two sections have al common cathode circuit, as will appear subsequently in this description.

The grid 46 of section is-connected to a ter-r minal 62 through a resistor 64 and a variable resistor 66. The anodes. 44 and 56 of the two sections are connected through resistors 68 and 10, respectively, to a terminal l2 at which a` regulated, positivepotential is indicated as being applied; Potential from this source is also applied througharesistor "i4 and variable resistor orpotentiometer- 76 to the grid 52 of section 2 ofthe relay tube.

The four gas tubes 30l to 36, inclusive, which may-be of-RCA Type 2D21, may-conveniently be thought of-vr as in two pairs,the pair constituted bytubes 30' and 3-2fbeingin'one channel and the pair constitutedby tubes 34 and 36; being in another-channel. The two channels are identical in construction and? arrangement, and the description ofA this part of the circuit will be confined, in the main, to the'upper channel of Figure 2. Corresponding elements in the upper and lower channels have been given the same reference-numerals, but are distinguished by the additional letters a and b, respectively.

The-tube 30 hasa cathode 88a,- an anode` 82a, a control grid 84a, and a fourth electrode 86a which serves as a shield aroundthe anode'to prevent ignition of the tubeby stray electrostatic elds and-is, therefore,` connected to the heatera by a conductorV 90a, and thus to ground; The,v tube 32 hassimila'rfelements 92a, 94a,96a, 98a, Milla and |0221 in the order named.

The cathodes *ofJ tubes 30 andv 34- are connected' nected tothe same! terminal-bya conductor ||4a.

Similarly, the anode. of tube 3411s connected-to a terminal |0811` through a resistor Hb and'conoluctor.A H212, and thecathode off tube 36 is connected tothe same terminalby a conductor I Mb. The two terminals |0811, |081) are connected through themotor 20 to a source of-alternating current, 'indicatedv at I6; of? the same frequency and phase as the alternating current applied to thecommon cathode circuit of the'relayv tube 28;

T he anode of section ofthe relay tube is connected to grid-84a of tube-30 through a couplingcapacitor |8a, and the anode-50 of ysection` 2 off` the relay tube is connected to*r grid 84h througha, coupling capacitor. H82). The grids alla,y 84h are alsoconnectedtoa'` terminal |20V through identical resistors .|22a, |221) anda variable resistor` |24, common to both channels.` At theterminalV |20 a negative biasingv potential'. is applied.

The, anode Vof tubell isconnectechto the` control grid of tube 32 by a resistor Illa and a time delay network consisting of resistors |26a, |28a and capacitors |360, and |32a, connected as shown in Figure 2. Similarly, the anode of tube 3Q is connected to the control grid of tube 3E by a resistor ||lb and a time delay network` |26b; |2813, |3611, |32b.

The operation of the circuit is as follows: The direct current voltage across the cathode resistor 26 of the power amplier IG in Figure l is a linear function of current flowing in the cathode circuit 2li. This voltage is applied between the input terminals 62 and 60 of Figure 2 in a polarity which makes the grid 4E of section of the relay tube 28 positive with respect to its cathode 42. The Variable resistor E6 in the grid circuit of section 2 is adjusted to place an equal or balancing positive voltage (from the source connected to terminal l2) on the grid 52 of section 2. The potential difference between each grid and its respective cathodeis, however, constantly Varying by reason of the alternatingvoltage appliedA to the common cathode circuit of the two sections from the source indicated at terminal 18. This variation is, therefore, the equivalent of an alternating signal applied to the grid of each section andfwill be amplified equally by each section byreason ofthe positive potentialsl applied to thetwo grids and anodes.

The signals, therefore, whichare applied! to the grids 84a and 8th ofthe rst two gas tubesv 3U and 3B from the anodes d4 and-5B oftherelay tube through the coupling capacitors ||8a and |I8b are equal to each other in magnitude` and phase, and are each an amplified replicaof the sixty cycle per second voltage applied at terminal 18.

The variable resistor: |24 is adjusted to place aA bias on the grids alla-and 84h suicient to preventr the tubes.l 30 and134 from conducting when these signalsfrom the relay-tube (in its balanced condition) are applied totheir grids- When the power amplifier IU of Figure 1 is no longer. at resonance, current in its anode-cathode circuit increases and the voltage across resistor 26 increases also.` This raises the potential of grid 46 with respect to cathode 42. and increases theamplication effected by section of the relay tube, and hence its anode current. The signal appliedtothe control grid of gas tube is, therefore, higherk thanu previously. The-increased anode current causes an increased Vpotential drop= across the common-cathode-resistor 56 and, therefore, reduces the amplification of section 2 ofthe relay tube. The-signal, therefore, appliedto grid'BAb-.of the gas tube 34 from anode 55E-'is thus less than it was previously. AV decrease in the-'applied directV current` signal` will cause an unbalance inthe opposite direction'with an increase in the voltage applied to gridedb and-a corresponding decrease. in the voltage applied to grid-84a.

It may be here pointedV out that while it' willv frequently be desirable. to balance the direct currentv voltage appliedto grid ll'vwith anequal F direct current voltage on grid-52'; Thisbalancing isnecessary only whenv the amplioation of the-twosections of the relay-tube is equal; because what is desired is that the alternating signalsapplied to-gridsA 84a, 8th-shall beequal but shall vary in opposite senses when thedirect ourrent signal appliedto.gridyaries It is withinthe scope of@ the invention to havethe ampliiication-of the two sections unequall and so tovary the direct: current potential 1 applied A to grid 52y (by adjustment of resistor- 16) as-to -have equalv currents flowing in the two anode circuits of the relay tube.

Similarly, while the operation of the two sections of the relay tube has been referred to as amplication, what is strictly desired is to produce two balanced replicas of the alternating signals applied at terminal 18. In some cases an unamplied, or even a reduced, replica may be desired. Conversely, if the amplification effected by each half of the relay tube is not suicient for any particular application, a further stage or stages of amplification may be inserted between the anode 44 and grid 84a and between anode 50 and grid 84D.

The operation of the gas tube circuit will now be described. When the direct current voltage applied to grid 46 increases, the alternating signal applied to grid 84a increases and the signal applied to grid 84h decreases.` Since this last grid was already biased (by adjustment of resistor |24) below ignition point, tube 34 will not conduct. In tube 30, however, the alternating voltage applied to grid 84a overcomes the biasing potential applied at terminal |20. This alternating voltage is in phase with the voltage applied to the anode of tube 30 through terminals I08a and I08b. The 2D21 tube is of a type which conducts when grid potential is above -3 volts with respect to cathode, and when anode potential is approximately 10 or l2 volts or greater with respect to the grid. The tube will, therefore, conduct during substantially the whole of the positive half cycle of anode voltage and will continue to conduct during each ensuing positive half cycle of anode voltage. Current will ilow in the anode circuit of tube 3U through the winding of motor 20, through conductor II2a and through resistor IIDa. This causes the end of resistor I Illa, which is more remote from the anode 82a, to be more positive than its end nearer that anode. The positive voltage thus created is applied to grid 96a of the second gas tube 32 through the delay network constituted by resistors I26a and I28a, and capacitors |3011 and I32a. The circuit parameters of the time delay network are chosen to create a delay of approximately The second gas tube 32 is connected to the alternating supply voltage source at IIB through conductors I I4a and I I2a and terminal I08a, and its anode is connected to ground through conductor I 66a. The anode voltage of tube 32 is, therefore, completely out of phase with that of tube 30. Because of the delay network through which it passes, at the time when the positive voltage derived from tube 3U and resistor IIUa is applied to the grid of tube 32, the anode of that tube is becoming more positive. The tube 32, therefore, conducts during the ensuing half cycle and during each half cycle when tube 30 is not conducting. Tubes 30 and 32 together, therefore, produce a full wave of substantial energy connected through terminal I08a and ground to drive motor 2D in one direction.

If the voltage across cathode resistor 26 de creases, then the signal applied to the grid of tube 34 rises and that applied to tube 30 falls. In this event, tubes 34 and 36 Will conduct, the full wave of energy will appear across terminal IIl8b and ground, and the motor 2|] will be driven in the opposite direction.

It was previously pointed out that the common cathode circuit of the relay tube includes a variable resistor 58. Adjustment of this resistor will determine the amount by which the grid-tocathode potential of section 2 will diverge from the grid-tofcathode potential of section I when current liowing through section I changes. It therefore determinesthe extent of the divergence between the alternating signals applied to the grid of tubes 30 and 34, respectively, and thus the sensitivity of the whole device. The variable resistor 66 in the grid circuit of section I serves to control the amount of positive potential derived from the cathode circuit of Figure 1 which is applied to the grid 4B.

It will be apparent that the embodiment of the invention thus far described has wider application than in the particular transmitter referred to. A direct current signal, however derived, may be applied to the circuit and any variation in that signal will res-ult in a full wave of alternating energy in the output circuit which may be used to drive a motor, or for such other purpose as may be desired. If an alternating signal is to be controlled, it may be rectified and integrated, if necessary, by methods known to the art, and the resulting direct current signal applied as here described. Any other condition which may be represented by a direct current signal (for example, light intercepted by a phototube) may be controlled in the manner described. It should also be noted that when either pair of gas tubes conducts, the current applied to terminals Ia, Ib is not proportional, or in any other Way a function of the variation in the original input signal. The device may be made as sensitive as desired by adjustment of resistor 58 as before explained. Once the tolerance limit desired has been exceeded, and immediately that occurs, one pair or other of the gas tubes will conduct and the full torque of the motor will be realized.

If the embodiment of the invention which is illustrated in Figure 3, the necessity for the balancing voltage which is applied to grid 52 in the embodiment of Figure 2 is dispensed with. Corresponding elements in Figures 2 and 3 have been given the same reference numerals and letters. In Figure 3, four resistors R1, R2, Re and R4 are connected in a Wheatstone bridge between anode and grid and between grid and cathode of the two sections of the relay tube 28, as shown in this figure. A voltage or other signal, distinguished by the letter E, is applied to the bridge and the condition for balance is that R1:R2=Rs:R4. The applied signal E in this embodiment may be alternating instead of direct current and may, if desired, be of radio frequency. The circuit illustrated may be employed, for example, in the production testing of resistors in which three of the four resistors constituting the arm of the bridge are fixed, and, say, Ri is the resistor under test. The tolerance limit would be set by adjustment of resistor 58, as in the previous embodiment. On a departure in the value of the resistor from the tolerance limit, the balance of the bridge will be disturbed, one of the two pairs of gas tubes will be actuated and the motor will operate to pass the resistor under test into one of two receptacles, depending on whether it is above or below a given value. In place of resistors, inductors or capacitors may be used for the arms of the bridge.

There has thus been described an electronic relay in which there is produced a pair of balanced, alternating currents which vary in opposite senses upon any variation in the controlled circuit. These voltages are, in turn, applied to a gas tube circuit so connected and energized as to produce a full wave of substantial energy in response to an increase in either of the voltages.

We claim as our invention:

'mams 'i'. An electronic relay operable on variation 'of adirect current signal from a given value to shift an alternating current from one channel to another, said relay comprising a pair of ampliners having a common cathode circuit, each of said ampliers having at least a control electrode in addition toa cathode and an anode, connections for applying said direct current signal to the control electrode of one of said amplifiers, connections for applying a balancing potential to the control electrode of the other of ysaid em'ipliers, connections including said common cathode circuit for applying an alternating voltage to'each of said ampliers, output means to be controlled having alternate alternating current channels, iirst and second gas tubes in each of said channels, each of said tubes having at least a cathode, an anode and a grid, a supply of alternating energy for said output means and said tubes of the same frequency as said alternating fzvoltage and in phase therewith, means for applying the output of said ampliiiers to the grids of said first tubes in said channels, respectively, and means for applying to the grids of said second gas tubes voltages delayed in time with respect to said alterhating energy.

2. A relay according to claim 1, characterized in that said common cathode circuit includes a variable resistor.

3. A D.-C. voltage responsive device comprising a pair of signal tubes, means to apply vthe D.C. voltage to which the circuit responds to at least one of said signal tubes to vary its gain with -respect to the other signal tube, an A.C. voltage source connected to have the voltage 4therefrom amplied respectively by eachof said signaltubes, two pair of gas tubes each pair being -connected respectively to one oi said control tubes to receivev the amplified A.C. voltage therefrom, said A.C. voltage source being connected to each pair of gas tubes, said gas tubes being interconnected in circuit tov give no rectification for equal amplitudes of said amplified voltages and to give vfull Wave rectication by the pair ofv gas tubes receiving the larger amplied voltage and not' by the other pair of gas tubes.

. 4. A D.C. voltage responsive circuit comprising two channels, each channel comprising a signal tube and a pair of gas tubes connected thereto to receive the output thereof, each `gas tube having a cathode-anode circuit, a connection from at least one of said signal tubes to said D.C. voltage source to receive said D.C. voltage vand to vary the gain of one of said signal tubes with respect to the other in response to said D.C. voltage, and an A.-'C. voltage source connected to be arnpliiied antiphasally by `said signal tubes to provide a signal output from each signal tube, said A.C. source being applied inthe cathode-anode circuit of one gas tube in Yeach channel and being applied antiphasally in the cathode-anode circuit of the other gas tube of each channel, `said gas Vtubes being interconnected, lwhereby said A.C.

voltage is full-wave rectified by the pair ci gas tubes receiving the larger Vamplified voltage of unequal amplified voltages.

5. The circuit claimed in claim 4, each said gas tube having a control element, the said gas tubes of each said channel havingv at least one control element connected to receive the ampliied output of the signal tube oi the ysaine channel.

6. The circuitc'laimied in claim 4, one of one pair of gas tubes in one channel having a cathode resistor in common with lone of Athe pair of gas tubes in the other channel, and the other of the pair of gas tubes in the other channel having a dierent cathode resistor in common with the other gastube of the otherpair.

J'. G. BEARD. ROBERT W. HARRLSON. ALEXANDER KREEITHEN.

REFERENCES CITED The following references are of record in the l'e ofY this patent:

UNITED STATES PATENTS Number Name Date 2,175,617 Cockrell Oct. 3, 1939 2,179,265 Luck Nov. 7, i939" 2,278,212 Moyer Mar. 31, 1942 2,427,688 Norgaard 1 Sept. 23, 1947 2,429,771 Roberts Q-- Oct. 28, 1947V 2,455,646 Beard etal Dec. 7, 1948 

